Dielectric or ferroelectric layers which react sensitively to hydrogen are used in many microelectronic structures. For example, in the case of metal-oxide-containing ferroelectric layers, the polarizability may be reduced and thereby the functioning of the ferroelectric layer may be restricted.
However, it is almost impossible to prevent the action of hydrogen in the fabrication of semiconductor products in the form of microelectronic structures. For example, the conditioning of the metallization and the transistors requires annealing steps in forming gas (95% N2, 5% W2). Furthermore, many layers are deposited in a hydrogen-containing atmosphere, for example tungsten and silicon nitride. In the case of ferroelectric layers, the action of hydrogen has been demonstrated t o adversely affect the electrical properties, in particular: to cause an increased leakage current, short circuits and lower polarization. If the ferroelectric layers are used as capacitor dielectric in a storage capacitor, the action of hydrogen can also lead to a reduction in the bonding of the ferroelectric layers and therefore the storage capacitors on the substrate.
To reduce the effect of hydrogen on hydrogen-sensitive layers, it has been proposed to apply what are known as hydrogen barrier layers to the hydrogen-sensitive layers, in order to protect the latter during subsequent process steps carried out in a hydrogen-containing atmosphere. In the case of storage capacitors, it is customary for the capacitor module to be covered by a hydrogen barrier layer, (encapsulation barrier layer, EBL).
For example, it is known from DE 199 04 379 A1 to cover the upper electrodes of a storage capacitor with a passivation layer and then with a hydrogen barrier layer. The passivation layer is intended to prevent the catalytic cracking of ammonia by the metal-containing upper electrode, which is required for deposition of the passivation layer. The catalytic cracking of ammonia leads to the direct release of hydrogen, which with an uncovered upper electrode, can diffuse through the latter to the capacitor dielectric. However, it has been found that although this passivation layer substantially prevents catalytic cracking of ammonia, it does not otherwise offer sufficient protection against the hydrogen which is inherently released by the deposition reaction.
It is also known from EP 0 513 894 A2 to apply a hydrogen barrier layer direct to the capacitor module and in particular to the edge regions of the capacitor electrodes, which are not covered by the ferroelectric layer. If the hydrogen barrier layer consists of an electrically conductive material, in accordance with EP0 513 894 A2 an insulating layer has to be provided between the hydrogen barrier layer and the capacitor module.
By contrast, in accordance with U.S. Pat. No. 6,027,947 the problem of hydrogen diffusion is supposed to be alleviated by encapsulating the upper capacitor electrode by means of the ferroelectric.
Furthermore, it has been found that during the deposition of the hydrogen barrier layers, not only is there a risk of the ferroelectric layer being contaminated by hydrogen, but also further problems are presented by the plasma which is used during the deposition of subsequent layers (e.g. hydrogen diffusion barrier, oxide layers). These difficulties may in particular involve electrostatic charging of the capacitor electrode and consequently damage to the ferroelectric layer.